1. Technical Field
The present invention relates to a light emitting device, a super-luminescent diode, and a projector.
2. Related Art
In order to realize a small-seized and high-luminance projector, it is required to improve the emission efficiency of a light source, and reduce the loss and the number of components of an optical system. By using a super luminescent diode (hereinafter also referred to as an “SLD”) as the light source, it is possible to eliminate a dichroic mirror necessary for a color separation optical system, and a rotary diffuser plate necessary to ensure the safety of a semiconductor laser and to reduce the speckle noise.
Further, there has been proposed a system (a backlight system) of disposing the SLD immediately below a light valve, and performing light collection and uniform illumination at the same time using microlenses in order to reduce the loss and the number of components of the optical system. In the case of the backlight system, for the sake of convenience of manufacturing accuracy of the microlenses, it is necessary to dispose the emission surfaces at intervals of about several hundreds micrometers through several millimeters. This can be realized by the SLD having a roughly bracket-shaped optical waveguide described in, for example, JP-A-2011-155103.
However, in such an SLD as described above, the light guided inside the active layer is amplified in an exponential manner toward the emission section side (the side with low reflectance). Therefore, on the emission section side, the carriers become short relatively to the light. Thus, the saturation of gain might occur, and the light output might be degraded in some cases.